The big fish lived in the Miocene, about 20 million years ago, and likely swam in shallow waters at mid-latitudes, in both the Atlantic and Pacific, the scientists wrote. They determined this by studying five tooth samples, which were found in California, North Carolina, Japan, and Peru. Those teeth were nearly two inches long. (See how the world's sharks stack up in size.)

The teeth also have a unique shape and mosaic-like structure that hasn’t been seen before, prompting the scientists to name the new species. Both front teeth, probably handy for grasping, and rear teeth, probably for slicing, were found.

Those teeth also enabled the scientists to estimate the body size of the fish, based on other known sharks. The result: about 12 feet long. That would make it a relatively big shark today, although a bit smaller than a great white, which can reach up to 20 feet long.

Still, people should take that estimate with a grain of salt, John-Paul Hodnett, a shark specialist at Saint Joseph's University in Philadelphia, told Live Science.

"For teeth, you should always be cautious of the fact that it is possible to have very large or small teeth in a shark's jaw, which do not represent the true aspect of the shark's body size," said Hodnett, who was not involved with the study.

The study also suggests the new species may have been a close relative of Carcharocles megalodon, which could grow up to 60 feet long. Both sharks should be placed in the extinct family Otodontidae, the scientists noted. (What killed the world’s biggest shark?)

The authors noted that fossil shark teeth are among the most commonly discovered types of vertebrate fossils, but they said few are as large as those belonging to Megalolamna paradoxodon. The species name alludes to the unusual nature of those teeth, which didn’t seem to fit any other known species.